This invention relates to polyarylene sulfide resin compositions having improved impact strength.
Polyarylene sulfide resins are attracting attention as high-performance engineering plastics having higher heat resistance, chemical resistance and rigidity than usual engineering plastics such as polycarbonate, polyacetal, nylon and polybutylene terephthalate. It is known that inclusion of a fibrous reinforcing material such as glass fibers into polyarylene sulfide leads to a striking improvement in the properties necessary for use as engineering plastics, such as strength, rigidity, toughness, heat resistance and dimensional stability. It is also known that with a glass fiber-reinforced polyarylene sulfide resin composition, the strength and rigidity increases generally with increasing amount of the glass fibers incorporated therein. Accordingly, when increased strength and rigidity are desired, it is the general practice to increase the amount of the glass fibers incorporated into the resin composition.
A relatively recent development has been the use of polyarylene sulfide compositions such as, for example, polyphenylene sulfide compositions, for molding electronic components and as encapsulating materials for electronic components. These compositions typically comprise glass fiber-reinforced polyarylene sulfide. Electronic components are molded or otherwise encapsulated to maintain electrical insulation, to provide mechanical protection and to otherwise shield the metallic components from exposure to the environment. As the evolution of electronics continues its rapid advance, it becomes increasingly important that the art and technology of molding and encapsulation keep pace.
Polyphenylene sulfide is useful in electronic applications such as in the formation of circuit boards, connectors and the like since polyphenylene sulfide can withstand the temperatures of vapor phase soldering which temperatures often are above 220.degree. C. without adversely effecting the properties of the molded resin such as blistering or dimensional distortion. Unfortunately, although polyphenylene sulfide has the necessary thermal stability for electronic applications, the material is relatively brittle and, thus, has low impact strength. Moreover, it is desirable to increase the glass fiber loading of the polyarylene sulfide for both cost reasons and for enhancing the strength and heat stability of the molded resin. Increasing the glass fiber content has an additional embrittling effect.
It is known to improve the impact strength of polyarylene sulfide by the addition of elastomeric materials thereto. Thus, U.S. Pat. No. 4,581,411 discloses improving the impact strength of polyarylene sulfide and glass-reinforced polyarylene sulfide by adding from about 0.1 to about 40 wt.% of a polymeric rubber which is selected from among silicon rubber, ethylene-acrylic rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, and poly(butylacrylate) rubber. It is also disclosed that further enhancement of the impact strength of the composition can be achieved when using either the silicon rubber or the poly(butylacrylate) rubber by adding small amounts of an organosilane.
U.S. Pat. No. 4,476,284 discloses polyarylene sulfide compositions which have improved physical properties including impact resistance by the inclusion therein of a thermoplastic elastomeric hydrogenated conjugated diene/monovinyl arene block polymer. The preferred hydrogenated conjugated diene/monvinyl aromatic block copolymers are isoprene/styrene or butadiene/styrene block copolymers. While the patent discloses that the desirable effects of the invention are found in the presence of any amount up to and over about 30% of the hydrogenated block copolymer, the preferred range is disclosed as from about 1-5% by weight.
U.S. Pat. No. 4,451,607 discloses increasing the crystallinity of polyarylene sulfide by blending therewith hydrogenated conjugated diene/monovinyl aromatic block copolymer in an amount up to about 5% by weight.
U. S. Pat. No. 4,628,072 discloses improving the impact strength of thermoplastic polymers, including polyarylene sulfide, by addition thereto of partially hydrogenated block copolymers of a monovinyl substituted aromatic hydrocarbon polymer and an olefin polymer block. The block copolymer has grafted thereto a unit containing a carboxylic acid group. As described in U.S. Pat. No. 4,783,503, the graft of the carboxylic acid group is attached by a process called "ENE reaction". Such modified block copolymers contain functional moieties only in the diene block, unlike the present invention. In addition, such modified block copolymers are deficient because the ENE reaction depends on unsaturation in the base polymer for reaction sites. A reasonable amount of residual unsaturation must be present in order to obtain an advantageous degree of functional moieties onto the base polymer. Since the ENE reaction cannot be carried out so that all double bonds on the base polymer are scavenged, the result of such a process is a modified block copolymer which contains too high a level of unsaturation for successful impact modification of high processing temperature thermoplastics.
The present invention is a further attempt to improve the impact strength of polyarylene sulfide articles without reducing the advantageous mechanical properties inherent in polyarylene sulfide, including polyphenylene sulfide. It is also an object of the present invention to improve the impact strength of glass-reinforced polyarylene sulfide compositions. Although not limited to one particular use, the present invention will find use in improving the impact strength of filled and unfilled polyarylene sulfide compositions which are used to mold and encapsulate electronic component parts.